Hitting the max Light Level possible.
As mentioned previously, Destiny 2 has two separate kinds of character progressions- an XP level, which is the more traditional kind of character level you are used to, and a Power Level, which is a composite average of the Attack and Defense ratings of your equipped gear.
Power Level has a soft level cap of 260- when you hit this, it is no longer possible for you to get it to go up in the ordinary way. However, you can still increase it to 300, which is the hard level cap. Just keep the following things in mind, to do once you have completed the campaign and hit the Level 20 cap: